A cuvette used for direct optical analysis of a fluid mixture is disclosed in U.S. Pat. No. 4,088,448. The cuvette according to this patent consists of a body having two flat surfaces spaced a predetermined distance from each other thereby forming an optical path and defining a cavity. The cavity has an inlet through which it communicates with the ambient atmosphere. The cavity has a predetermined fixed volume, and the predetermined distance between the surfaces enables the cavity to take up a sample by capillary action. Further, a reagent is applied to the surfaces of the cavity.
This cuvette offers many advantages over prior art apparatuses of this kind. A fluid can be taken up into the cuvette for mixing and chemical reaction with a suitable reagent, e.g. for color development in the same cavity used for a subsequent measuring operation. Thus, the cuvette disclosed in U.S. Pat. No. 4,088,448 simplifies the sampling procedure, reduces the amount of accessory equipment, and in most cases--depending on the type of analysis--considerably increases the accuracy of the analysis since the analysis procedure is independent of the level of skill of those carrying out the analysis.
U.S. Pat. No. 4,654,197 discloses a cuvette which by using a semipermeable membrane as part of the cuvette, increases the number of reactions possible in the cuvette system.
U.S. application Ser. No. 768,321, filed Oct. 17, 1991, now U.S. Pat. No. 5,286,454 discloses a cuvette for taking up at least one fluid and for mixing a fluid with a dry reagent for analyzing a mixture, wherein the cuvette comprises:
a) at least one capillary first cavity having an inlet and constructed and arranged to take up a fluid in capillary action alone; PA1 b) a first channel having a non-capillary and non-spontaneous fluid transporting function operative only under external influence by application of a centrifugal force on the cuvette; PA1 c) a centrifugation reception cavity communicating with the at least one capillary first cavity via the first channel and constructed and arranged to exert no capillary action; PA1 d) at least one capillary second cavity constructed and arranged to take up a fluid by capillary force alone; and PA1 e) a first capillary transporting means projecting into the centrifugation reception cavity, being connected to the at least one capillary second cavity and constructed and arranged to transport fluid by capillary action from the centrifugal reception cavity into the at least one capillary second cavity. The centrifugation reception cavity can be divided into two sections: a first, lower section for receiving heavy material for taking up the fluid, and a second, upper section which serves as a measuring cavity.
Instead of relying on centrifugal force for fluid transport through the channel, it is possible to exert a pressure on the fluid in the first cavity. In this case a venting device is necessary. The walls of the various channels, or desired portions thereof, may be coated with reagent, and an analysis can be carried out on fluid in both the first cavity and the second or the capillary section of the reception cavity, and also in the heavier-material section of the reception cavity.
From U.S. Pat. Nos. 4,462,964 and 4,714,590 it is known to provide capillary orifices in the fluid path of a cuvette used of analyses. Contrary to the arrangement of the present invention, these orifices serve to prevent fluid transport until the cuvette is subjected to centrifugation.